1. Field of Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device having a high aperture ratio and a method of manufacturing thereof.
2. Discussion of Related Art
Since twisted nematic liquid crystal display devices (TN-LCDs) have a high image quality and a low electric power consumption, they are widely applied to flat panel display devices. TN-LCDs, however, have a narrow viewing angle due to refractive anisotropy of liquid crystal molecules. This is because before voltage is applied, the liquid crystal molecules are horizontally aligned and the liquid crystal molecules become nearly vertically aligned with respect to a substrate when voltage is applied to a liquid crystal panel.
Recently, in-plane switching mode liquid crystal display devices (IPS-LCDs) have been widely studied in which viewing angle characteristic is improved and the liquid crystal molecules are nearly horizontally aligned.
FIG. 1A is a plan view of a unit pixel of a conventional in-plane switching mode active matrix liquid crystal display (AM-LCD). FIG. 1B is a sectional view according to line I–I′ of FIG. 1A.
Referring to the drawings, a unit pixel region is defined by a gate bus line 1 and a data bus line 2 in which the lines are arranged perpendicularly and/or horizontally as a matrix shape on a first substrate 10. A common line 16 is arranged parallel to the gate bus line 1 in the pixel region and the thin film transistor (TFT) is formed where the data bus line 2 and the gate bus line 1 cross each other. The TFT includes a gate electrode 3, a gate insulator 19, a semiconductor layer 12, an ohmic contact layer 13, source electrode 4a and drain electrode 4b in which the gate electrode 3 is connected to the gate bus line 1, and source and drain electrodes 4a and 4b are connected to the data bus line 2, and the gate insulator 19 is formed on the entire surface of the first substrate 10.
A common electrode 7 and a data electrode 8 are formed in the pixel region. The common electrode 7 is formed with the gate electrode 3 and connected to the common line 16, and the data electrode 8 is formed with the source and drain electrodes 4a and 4b and electrically connected to them. Further, a passivation layer 22 and a first alignment layer (not illustrated) are deposited on the entire surface of the first substrate 10.
On a second substrate 11, a black matrix 15 is formed to prevent light leakage which may be generated around a TFT, the gate bus line 1, and the data bus line 2. A color filter layer 25 and a second alignment layer (not illustrated) are formed on the black matrix 15 in sequence. Also, a liquid crystal layer 30 is formed between the first and second substrates 10 and 11.
When no voltage is applied to LCD having the above structure, liquid crystal molecules in the liquid crystal layer 30 are aligned according to alignment directions of the first and second alignment layers, but when voltage is applied between the common electrode 7 and the data electrode 8, the liquid crystal molecules are aligned parallel to extending directions of the common and data electrode. As in the foregoing, since liquid crystal molecules in the liquid crystal layer 30 are switched on the same plane at all times, grey inversion is not created in the viewing angle directions of up and down, and right and left directions.
FIG. 2A is a plan view of the part forming the storage capacitor line of the conventional LCD. FIG. 2B is a sectional view according to line II–II′ of FIG. 2A.
Referring to the drawings, the gate insulator 19 and the semiconductor layer 12 are deposited on the gate lines 1 and a storage capacitor line 5. The data bus line 2 is coupled to the storage capacitor line 5 through a hole 18 of the gate insulator 19 and formed with the source and drain electrodes 4a and 4b of FIG. 1A. A method for manufacturing the LCD having the above structure is described in FIG. 3.
A TFT region describes a sectional region according to line I–I′ of FIG. 1A, and a storage region describes a sectional region according to line II–II′ of FIG. 2A.
As shown in the drawing, a method of manufacturing the conventional LCD comprises patterning the gate electrode 3, the common electrode 7, and the storage capacitor line 5 (S1), patterning the semiconductor layer 12 and the ohmic contact layer 13 after forming the gate insulator 19, the semiconductor layer 12, and the ohmic contact layer 13 on the gate electrode 3 (S2), forming the hole 18 by opening some part of the gate insulator 19 in the part forming the storage capacitor line 5 (S3), patterning the source and drain electrodes 4a and 4b, the data electrode 8, and the data bus line 2 on the ohmic contact layer 13 and the gate insulator 19 (S4), forming the passivation layer 22 after n+ dry etching (S5).
However, in the conventional LCD, it is necessary that each of the storage capacitor lines and pad open regions are formed respectively, and the storage capacitor lines are coupled to each other by the data bus line when the gate insulator is patterned to form the storage capacitor line.